• Proceedings of the KSME Conference
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• 2005.11a
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• pp.49.2-49.2
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• 2005

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2545-2556
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• 2024

In the present study, we investigated the velocity distribution, temperature distribution and condensation characteristics of steam jet issuing from four different orifice nozzles with a Reynolds number of approximately 79,000 using the phase Doppler particle analyzer system and a K-type thermocouple. The steam jet discharged from the orifice nozzle has a wider jet width compared to pipe nozzle because of the vena-contracta which can enhance the mixing of steam jet with the ambient air. Therefore, the orifice jet showed less condensation due to its wideness, resulting in small velocity decay rate and large temperature decay rate due to momentum conservation and decreased latent heat release compared to pipe nozzle, respectively. Also, the wider jet width of the orifice jet resulted in larger velocity and temperature spread rate compared to the pipe jet. In addition, the increase in the aspect ratio of the orifice jet led to more condensation and larger velocity spread rate and temperature spread rate due to both the vena-contracta and axis-switching effect, resulting in the increase of jet entrainment.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.1-9
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• 2012

The gas jet from a coaxial porous injector for two-phase flows is discharged from the porous surface, which encloses the center liquid jet, and the gas and liquid jet interact with each other physically. The wall injected gas jet transfers the radial momentum effectively while the radial gas jet develops to axial jet, and the performance of atomizing and mixing can be improved. In this study, the Weber number and the ratio of momentum flux were controlled by changing the gas injection area and the mass flow rate of the gas jet, and a study on the spray characteristics at the cold-flow test using water and air simulant was performed. It is concluded that the radial momentum transfer concept of a coaxial porous injector gives a positive effect on the atomization and mixing of the two-phase spray.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.132-142
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• 2000

The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.646-655
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• 2001

This paper reports the effects of nozzle exit boundary layer swirl on the instability modes of underexpanded supersonic jets emerging from plane rectangular nozzles. The effects of boundary layer swirl at the nozzle exit on thrust and mixing of supersonic rectangular jets are also considered. The previous study was performed with a 30°boundary layer swirl (S=0.41) in a plane rectangular nozzle exit. At this study, a 45°boundary layer swirl (S=1.0) is applied in a plane rectangular nozzle exit. A three-dimensional unsteady compressible Reynolds-Averaged Navier-Stokes code with Baldwin-Lomax and Chiens $\kappa$-$\xi$ two-equation turbulence models was used for numerical simulation. A shock adaptive grid system was applied to enhance shock resolution. The nozzle aspect ratio used in this study was 5.0, and the fully-expanded jet Mach number was 1.526. The \"flapping\" and \"pumping\" oscillations were observed in the jets small dimension at frequencies of about 3,900Hz and 7,800Hz, respectively. In the jets large dimension, \"spanwise\" oscillations at the same frequency as the small dimensions \"flapping\" oscillations were captured. As reported before with a 30°nozzle exit boundary layer swirl, the induction of 45°swirl to the nozzle exit boundary layer also strongly enhances jet mixing with the reduction of thrust by 10%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.1011-1016
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• 2008

Jet-A spray and combustion were numerically analyzed in annular type combustor model using KIVA3V. The combustor geometry have 6 dilute holes. Swirl effect and thermal NO were considered in this investigation to analyze mixing and combustion characteristics. Fuel vapor, flame temperature, NO generation were investigated for various spray angle. As increase of spray angle, Jet-A vapor appeared uniformly in primary zone and evaporation rate was increased. Mixing between fuel vapor and ambient gas was enhanced as increase of spray angle. As a result, high temperature region appeared widely and thermal NO generation rate was increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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• pp.1013-1021
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• 1998

Various vortical structures are investigated by using three kinds of flow visualization methods in branch pipe flows. There are two typical flow patterns when a jet from the branch pipe with various angles is injected to the main pipe cross flow. The velocity range of cross flow of the main pipe is 0.2 m/s ~ 1.2 m/s and the corresponding Reynolds number, R$_{p}$ is of the range 1.5 * 10$^{3}$ ~ 9.02 * 10$^{3}$. The velocity ratio(R), jet velocity/cross flow velocity, is chosen from 1.3 to 4. The subsequent behavior and development of the ring vortices which are created at the jet boundary mainly depend on the velocity ratio. An empirical relation for the shedding frequency of the ring vortices is derived. It is also found that there are two different vortex shedding mechanism in the mixing of two fluid streams.s.

• Journal of ILASS-Korea
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• v.9 no.2
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• pp.34-40
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• 2004

In a liquid-fueled ramjet engine, the insufficient mixing and evaporation result in the low combustion efficiency and combustion instability. Improving its characteristics and devising a means of fuel droplets with air may compensate these disadvantages of liquid fuel ramjet engine. The jet penetrations of various fuel injectors were measured to investigate the spray characteristics of a liquid-fueled ramjet engine under high pressure air-stream conditions. The penetrations in high pressure conditions are smaller than the values calculated from Inamura's or Lee's equations, and the jet penetrations in the high pressure conditions have a similar tendency. In the dual orifice injectors, the jet penetrations of rare orifice is rapidly increased due to the reduction of the drag, which is created by the jet column of front orifice. The jet penetration of rare orifice is increased because of the drag reduction created by the jet column of the front orifice. Because of the drag reduction formed by the column of jet, the jet penetration in the rear orifice of dual orifice injector is much larger than the jet penetrations of single orifice injector. As the distances of the orifice are increased, the jet penetrations of the rear orifice decrease.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.33-38
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• 2000

The characteristics of center-driver jet pump which have multi-nozzle were studied in this research. Jet nozzles are connected outside of the bend rather than inserted in the bend in order to transport solid materials or fish without any harm. Jet pumps having one nozzle, two nozzles, four nozzles, and sixteen nozzles were tested in this study. The efficiencies and performances of jet pumps were studied for several nozzles shape, for three different mixing chamber shapes, for two suction area shapes. All the efficiency curves for these cases are presented in this paper.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1472-1479
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• 2003

An attempt to reduce supersonic jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10 mm. Two micro-nozzles with an inside diameter of 1 mm each are installed on the exit plane at an angle of 45 relative to the main jet axis. Far-field noise was measured at 40 diameters off the jet axis. The angle between a microphone and the jet axis is 30 or 90$^{\circ}$. For an injection rate of 4-6% of the main jet, screech tones were completely suppressed by the microjets. The reduction in the overall sound pressure levels were 2.4 and 2.7 dB for 90 and 30 measuring directions, respectively. However, the enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or deformed large scale vortical structures by the microjets.